Did you know how many factors effects your page rank in google search, here is some information about these things which is published by one of the Google employee.
Matt Cutts a software engineer who joined in Google in January 2000 and now the head of Google’s Webspam team says that Google uses 200 different signals when ranking pages and also makes hundreds of changes each year and in terms of variables, it’s possible that 10K variables could be reached.
You can read The Anatomy of a Large-Scale Hypertextual Web Search Engine original Stanford paper which is wrote by Sergey Brin and Lawrence Page.